Polymer brushes for extreme ultraviolet photolithography

ABSTRACT

A polymer brush with a plurality of repeat units wherein some portions of the repeat units have one or more grafting groups and some portions have one or more interface tuning groups is disclosed. The grafting groups are selected based on the identity of an inorganic substrate, and the interface tuning groups are selected based on the identity of a photoresist that will interact with the groups. A process of lithographic patterning and an electronic device comprising at least one integrated circuit formed by the process of lithographic patterning are disclosed as well. The process comprises providing an inorganic substrate, depositing the disclosed polymer brush onto the inorganic substrate, and depositing a photoresist onto the polymer brush. The process further comprises masking the photoresist with a photomask having a pattern, and applying energy to the masked photoresist to form an etch mask. The inorganic substrate is then etched.

BACKGROUND

The present disclosure relates to lithographic materials for extremeultraviolet (EUV) lithography and, more specifically, polymer brushesfor mediating interfacial interactions between photoresists andinorganic substrates.

Extreme ultraviolet (EUV) lithography is a lithographic technique usedin semiconductor fabrication that employs extreme ultraviolet light totransfer a pattern from a photomask to a resist. The pattern is thentransferred from the resist to a hardmask through etching, and from thehardmask to a semiconductor material through additional etching. EUVlight has wavelengths of approximately 124-10 nm, which are close to theX-ray region. The short wavelengths provided by EUV light allow for highresolution patterning in semiconductor fabrication.

SUMMARY

Various embodiments are directed to a polymer brush comprising aplurality of repeat units, portions of the plurality of repeat unitshaving one or more grafting groups, one or more interface tuning groups,and optionally one or more cleavable groups. The grafting groups areselected based on the identity of an inorganic substrate, such as aninorganic hardmask, to which the groups will bind. Examples of graftinggroups can include alkynes, primary hydroxyls, secondary hydroxyls,acrylic acids, epoxies, alkenes, phosphonic acids, propargyls,phosphonic esters, amines, carboxylic acids, and alkoxysilanes. Examplesof inorganic hardmask materials can include silicon, titanium nitride,titanium oxides, titanium oxynitrides, tantalum nitride, hafnium oxides,niobium nitride, lanthanum oxide, silicon oxides, silicon oxynitrides,zirconium oxides, and tin oxides. The interface tuning groups areselected based on the identity of a photoresist that will interact withthe groups. Examples of tuning groups can include acidic groups, phenylgroups, methoxy groups, ethylene groups, hydrogen atoms, methyl groups,and trifluoromethyl groups.

Further embodiments are directed to a process of lithographicpatterning. The process can comprise providing an inorganic substrate,such as an ultrathin inorganic hardmask, depositing a polymer brush ontothe inorganic substrate, and depositing a photoresist onto the polymerbrush. The polymer brush can comprise a plurality of repeat units,portions of the plurality of repeat units having one or more graftinggroups, one or more interface tuning groups, and optionally one or morecleavable groups. Examples of photoresists can include acrylicphotoresist, phenolic photoresists, and hybrid photoresists. The processcan further comprise masking the photoresist with a photomask having apattern. Energy, such as extreme ultraviolet light, can be applied tothe masked photoresist. This energy can come from a laser-driven tin(Sn) plasma. An etch mask can then be formed by developing thephotoresist. The pattern is then transferred to the inorganic substrateby etching the portions of the inorganic substrate that are exposed bythe etch mask.

Additional embodiments are directed to an electronic device comprisingat least one integrated circuit chip prepared in an extreme ultravioletlithographic patterning process. The electronic device can furthercomprise at least one additional integrated circuit chip. The extremeultraviolet lithographic patterning process can comprise providing aninorganic substrate, depositing a polymer brush onto the inorganicsubstrate, and depositing a photoresist onto the polymer brush. Thepolymer brush can comprise a plurality of repeat units, portions of theplurality of repeat units having one or more grafting groups, one ormore interface tuning groups, and optionally one or more cleavablegroups. The process can further comprise masking the photoresist with aphotomask having a pattern. Extreme ultraviolet light can be applied tothe masked photoresist. An etch mask can then be formed by developingthe photoresist. The pattern can then be transferred to the inorganicsubstrate by etching the portions of the inorganic substrate that areexposed by the etch mask.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a stack of layers for extremeultraviolet (EUV) lithographic patterning, according to some embodimentsof the present disclosure

FIG. 2 is a flow diagram illustrating a process of forming a polymerbrush that mediates adhesion of a photoresist to an inorganic hardmask,according to some embodiments of the present disclosure.

FIG. 3 is a diagrammatic representation of block structures of threeexamples of generic polymer brushes, according to some embodiments ofthe present disclosure.

FIG. 4 is a diagrammatic representation of the molecular structures offour examples of polymer brushes, according to some embodiments of thepresent disclosure.

FIG. 5A is a chemical reaction diagram illustrating processes of formingtwo polymer brushes, according to some embodiments of the presentdisclosure.

FIG. 5B is a chemical reaction diagram illustrating a process ofgrafting a polymer brush to an inorganic hardmask, and a process ofcleaving the polymer brush from the inorganic hardmask, according tosome embodiments of the present disclosure.

DETAILED DESCRIPTION

Photolithography is a technique commonly used in semiconductorfabrication to etch integrated circuit patterns onto semiconductingwafers. Photolithographic patterning involves coating a base materialwith a photosensitive resist material, which is referred to herein as aphotoresist. The photoresist is selectively masked by a photomask thatis designed with the pattern to be etched onto the semiconductor. Anenergy source, such as electromagnetic radiation or an electron beam, isapplied. The unmasked sections of the photoresist are exposed to theenergy source. When the photoresist is exposed to the energy source, achemical reaction occurs so that selected sections of the photoresistare dissolvable in a developer, and therefore removable during adevelopment stage in the lithographic process. Removing the dissolvablesections during the development stage creates the patterned photoresist.The patterned photoresist can also be referred to as an “etch mask.” Thepattern can be transferred from the etch mask to semiconductor or othersubstrate materials during subsequent etching steps. In these step, theparts of the substrate that are not covered by the etch mask are etched.

The locations of the dissolvable sections of the photoresist depend uponthe selection of photoresist material and developer. The developer is asolvent in which the photoresist is immersed after exposure to theenergy source. Immersion in the developer allows the dissolvablesections of the photoresist to be removed. Removal can be aided byrinsing with a solvent after development. Photoresists can becategorized as either positive photoresists or negative photoresists.When a positive photoresist is exposed to negative tone development, thesections of the photoresist that were not exposed to the energy source(i.e., the masked sections) are soluble in the developer. However, whena positive photoresist is exposed to positive tone development, thesections that were exposed to the energy source (i.e., the unmaskedsections) are soluble in the developer.

Traditionally, the electromagnetic radiation emitted by the energysource used in the photolithographic process has had wavelengths in theregion of 436 nm (blue light), 365 nm (near ultraviolet (UV)), or248-193 nm (deep UV). Feature sizes in a pattern to be printed on asemiconductor are, in part, dependent on the wavelength of radiationused. That is, the smallest printable features are limited by theshortest wavelength produced by the energy source. As technologyprogresses to require smaller devices with a greater number ofintegrated circuits, shorter wavelengths become more desirable.Therefore, various types of next-generation lithography techniques thatcan provide these shorter wavelengths are being explored and developed.

One type of next-generation lithography is a photolithographic techniquecalled extreme ultraviolet (EUV) lithography. EUV lithography employslight in the 124-10 nm (EUV) region. For high-resolution patterning insemiconductor fabrication, an EUV wavelength of about 13.5-10 nm,generated by a laser-driven tin (Sn) plasma source, is often used. Thishigh-resolution patterning is generally carried out with positivephotoresists that are exposed to positive tone development, but positivephotoresists and negative tone development can be used as well. However,while EUV lithography allows for the production of smaller semiconductorchips, there are challenges associated with its use.

One of these challenges arises in the adhesion of the photoresist to theunderlying base material, or substrate (e.g., an inorganic hardmask(HM), metal, semiconductor material, etc.). For example, when usingsmall-dimensioned patterns, capillary forces can be greater than theadhesive interactions between the photoresist and the substrate. Whenthe photoresist does not adhere properly to the substrate, patterncollapse can occur. Additionally, if residue from the photoresist isleft behind after development and rinsing, the pattern can be disrupted.Thus, techniques for attaining stable adhesion and absence of residuebetween the photoresist and the underlying substrate withoutnecessitating additional expensive and/or time-consuming processingsteps are of interest.

Polymer brushes designed to mediate interfacial interactions between aphotoresist and an inorganic substrate are disclosed herein. Thismediation results in improved adhesion in some embodiments. A polymerbrush is a polymer macromolecule having repeat units with at least onefunctional group that can be grafted (i.e., covalently bonded) to asubstrate. The polymer brushes disclosed herein are grafted to thesurface of the inorganic substrate, and mediate its interaction with thephotoresist. The polymer brushes can be synthesized by thepolymerization of a variety of monomers. The identity of the monomersdetermines the properties and reactivity of the polymer brush. Themonomers can have functional groups for grafting to a variety ofinorganic materials, functional groups that allow the polymer to becleaved from the grafting group, functional groups that interact withthe photoresist, functional groups that interact with solvents anddevelopers, functional groups that harvest photons, etc. Further, thepolymer brushes disclosed herein can be formulated in a spin-castablesolvent, and therefore do not introduce significant processingcomplexity or expense.

FIG. 1 is a schematic diagram 100 illustrating a stack of layers 104,108, 112, and 116 for EUV lithographic patterning, according to someembodiments of the present disclosure. The stack includes a polymerbrush 104 between a photoresist 108 and an inorganic hardmask 112 thatis on a semiconductor wafer 116. While the polymer brush 104 isillustrated as being bonded to an inorganic hardmask 112 over asemiconductor wafer 116, additional layers may be present in someembodiments. For example, an organic underlayer (e.g., carbon or apolymer) and/or a dielectric layer (e.g., silicon dioxide or siliconoxynitride) can be included. Processes of forming the layers 104, 108,112, and 116 are discussed in greater detail with respect to FIG. 2.

Examples of photoresist layers 108 can include phenolic, acrylic, orhybrid (phenolic-acrylic) chemically amplified photoresists. Examples ofphenolic photoresists can include polyoxybenzylmethylenglycolanhydride(Bakelite), cresol formaldehyde novolac resins, copolymers ofpolyhydroxystyrene modified with a ketal-based protecting group or atert-butyloxycarbonyl protecting group, etc. Examples of acrylicphotoresists can include poly(methyl methacrylate) (PMMA), polyacrylate,norbornane lactone methacrylate (NLM)/methyl adamantane methacrylate(MAdMA) copolymers, etc. Hybrid photoresists are polymers that combinephenolic and acrylic monomers such as polyhydroxystyrene/MAdMAcopolymers.

In some embodiments, the photoresist 108 is prepared by dissolving thephenolic, acrylic, or hybrid monomers in an organic solvent (e.g.,propylene glycol monomethyl ether acetate or cyclohexanone), and addinga suitable photoacid generator (e.g., triphenylsulfoniumperfluorobutanesulfonate) and base quencher (e.g., tetrabutylammoniumlactate). However, commercially available or pre-prepared photoresistscan also be used. In some embodiments, the thickness of the photoresistranges from approximately 30 nm to 50 nm, though it can range fromapproximately 1 nm to 500 μm.

The photoresist 108 adheres to the polymer brush 104, which is graftedto the inorganic hardmask 112. The polymer brush has repeat units thatare determined by the identity of the monomers polymerized. The repeatunits are functionalized with groups that affect the properties andinteractions of the polymer brush 104, such as grafting, interfaceinteractions with the photoresist, and cleavability. Examples of polymerbrushes can include vinyl polymers, epoxy polymers, polyester polymers,polyurethane polymers, polyamide polymers, polycarbonate polymers,polyurea polymers, polyether polymers, polyimide polymers, etc. In someembodiments, the average molecular weight of the polymer brushes is in arange of 2,000 to 10,000 Da (g/mol). However, the average molecularweights of the polymer brushes can, in some embodiments, be within arange of 400 to 10,000,000 Da.

The polymer brush 104 includes repeat units with at least one functionalgroup capable of grafting to the inorganic hardmask 112 in one or morelocations. The functional group that binds to the inorganic hardmask 112is referred to herein as a “grafting group.” Examples of grafting groupscan include alkynes, primary hydroxyls, secondary hydroxyls, acrylicacids, epoxies, alkenes, phosphonic acids, propargyls, phosphonicesters, amines, carboxylic acids, alkoxysilanes, etc. The selection ofgrafting group is based, at least in part, on the reactivity between thegrafting group and the underlying substrate. This is discussed ingreater detail with respect to FIG. 2.

The polymer brush 104 also includes repeat units with least one tunablefunctional group that interacts with the photoresist 108. Thisfunctional group is referred to herein as an “interface tuning group.”Tuning the functional group refers to selecting the functional groupbased on its properties (e.g., charge, acidity, size, polarity, etc.).Examples of this interaction can include promoting photoresist adhesion,increasing photon harvesting, improving photoresist performance, etc.The interface tuning groups can also affect the surface energy orcontact angle with water of the polymer brush 104. Examples of interfacetuning groups can include acidic groups (e.g., phenol, sulfonic acid,fluorosulfonic acid, carboxylic acids, acrylic acids, etc.), phenylgroups, methoxy groups, ethylene groups, hydrogen atoms, methyl groups,trifluoromethyl groups, etc.

Additionally, the polymer brush 104 can optionally include repeat unitshaving functional groups capable of being cleaved in a later reaction.This functional group is referred to herein as a “cleavable group.” Insome embodiments, the cleavable group is a tertiary ester. Additionalexamples of cleavable groups can include primary and secondary esters,sulfate esters, phosphate esters, etc. Methods of cleaving the polymerbrush 104 can include applying heat, acid, photons, etc. For example, amethyl ester cleavable group can be cleaved when exposed to 172 nm lightand a developer solution. In addition, cleaving can be accomplished witha combination of two or more cleaving methods. Cleaving the polymerbrush 104 from the surface of an inorganic hardmask 112 enablesreworking or wet etching of the hardmask 112. Additionally, cleaving canreduce the amount of residue left behind by the photoresist 108, therebypreventing pattern disruption or scumming caused by the residue.

The inorganic hardmask (HM) 112 to which the polymer brush 104 isgrafted can be composed of various materials. In some embodiments, theinorganic HM 112 is a transition metal oxide or lanthanide oxide. Theinorganic HM 112 can also be a transition metal nitride or lanthanidenitride. Further, the inorganic HM 112 can be a transition metaloxynitride or lanthanide oxynitride. Examples of these inorganic HM 112materials can include silicon, titanium nitride (TiN), titanium oxides(TiO_(x)), titanium oxynitrides (TiO_(x)N_(y)), tantalum nitride (TaN),hafnium oxides (HfO_(x)), niobium nitride (NbN), lanthanum oxide(La₂O₃), low temperature oxides (LTOs), silicon oxides (SiO_(x)),silicon oxynitrides (SiO_(x)N_(y)), zirconium oxides (ZrO_(x)), tinoxides (SnO_(x)), etc. In the preceding chemical formulas, “x” and “y”represent the number of oxygen or nitrogen atoms (e.g., 1, 2, or 3atoms), respectively. In some embodiments, the inorganic HM 112 is anultrathin hardmask (i.e., an inorganic hardmask with a thickness of lessthan or equal to approximately 5 nm).

A pattern created on the photoresist is transferred onto the inorganichardmask 112, and then onto the semiconductor wafer 116. This transferinvolves etching the sections of the substrate that were removed duringdevelopment of the photoresist. The transfer can optionally involvesteps in which the pattern is transferred onto layers between theinorganic HM 112 and semiconductor wafer 116 first. This is discussed ingreater detail above. Examples of semiconductor wafer 116 materials caninclude silicon (Si), germanium (Ge), silicon-germanium (Si—Ge),graphene, organic semiconductors, silicon carbide (SiC), galliumarsenide (GaAs), gallium nitride (GaN), indium gallium arsenide(InGaAs), etc. The silicon can be amorphous silicon (aSi), crystallinesilicon (cSi), or polycrystalline silicon (poly-Si).

FIG. 2 is a flow diagram illustrating a process 200 of forming a polymerbrush 104 that mediates adhesion of a photoresist 108 to an inorganichardmask 112, according to some embodiments of the present disclosure.The polymer brush 104 is formed by the polymerization of one or moretypes of monomer. This is illustrated at step 204. Examples of monomersthat can be polymerized in the synthesis of the polymer brush 104 caninclude acrylate esters, acryl amide, methacrylate esters, methacrylamides, vinyl esters, vinyl ethers, olefins, etc. The monomers can besubstituted and/or unsubstituted. In some embodiments, the polymer brush104 is formed by polymerization of a diol compound and a diisocyanate,condensation polymerization of a diol compound or a diamine compound anda dicarboxylic acid, ring-opening polymerization of a lactone or alactam, condensation polymerization of an aminocarboxylic acid, etc.

The monomers that will form the polymer brush 104 are selected based onthe desired properties of the resulting polymer brush 104. Monomers thatinclude at least one grafting group, at least one interface tuninggroup, and optionally at least one cleavable group are polymerized toform the polymer brush. In some embodiments, each of these functionalgroups are on different types of monomer. However, monomers that includetwo or more of the functional groups can also be used. For example, onetype of monomer could include two grafting groups or one grafting groupand one interface tuning group. Additionally, the functional groups canform during the polymerization process or in subsequent reactions,rather than being initially bound to the monomers.

The polymer brush 104 can be made from the polymerization of one type ofmonomer, or from the polymerization of two or more types of monomer. Forexample, a polymer brush 104 could be made from a type of monomer thathas both a grafting group and an interface tuning group. The polymerbrush 104 could also be made of one type of monomer that has only agrafting group and one type of monomer that has only an interface tuninggroup. Polymerizing one type of monomer results in a homopolymer (i.e.,a polymer having one type of repeat unit), while polymerizing two ormore types of monomer results in a copolymer (i.e., a polymer having twoor more types of repeat unit). Examples of the structures and synthesesof polymer brushes are discussed in greater detail with respect to FIGS.3, 4, and 5A.

In some embodiments, the choice of grafting group is based upon theinorganic hardmask (HM) 112 to which it will form a stable bond. Forexample, phosphonic acid grafting groups will bind to metal oxides(e.g., TiO_(x), La₂O₃, HfO_(x), ZrO_(x), SnO_(x), etc.), and terminalalkyne or alkene grafting groups will bind to silicon surfaces (e.g.,aSi, cSi, poly-Si, silicon hydrides, etc.). Additional examples ofgrafting groups that bind to metal oxides can include phosphonic esters,hydroxyls, alkoxysilanes, etc. Hydroxyl grafting groups are often usedwhen the inorganic HM 112 material is a silicon oxide (SiO_(x)) orsilicon oxynitride (SiO_(x)N_(y)). Further, acidic grafting groups(e.g., phosphonic acid, carboxylic acid, acrylic acid, etc.) will bindto SiN surfaces, and alkene grafting groups will bind to metal oxidessuch as TiO₂, ZnO, ZrO₂, SnO₂.

The polymer brush 104 is deposited onto the inorganic HM 112 substrate.This is illustrated at step 208. A mixture containing the polymer brush104 in an organic solvent is prepared. In some embodiments, the polymerbrush 104 is prepared in this organic solvent. Examples of organicsolvents that can be used can include propylene glycol monomethyl etheracetate (PGMEA), propylene glycol methyl ether (PGME),4-methyl-2-pentanol (4M2P), cyclohexanone (CHX), ethyl 3-epoxypropionate(EEP), n-butyl acetate (nBA), etc. A layer of the solvent/polymermixture is deposited onto the substrate by spin casting or spin coating.The coated substrate is then baked at a temperature ranging fromapproximately 18° C. to 350° C. in order to remove the solvent, and topromote the bonding of the grafting groups to the substrate surface. Anynon-grafted portions of the polymer brush can be removed by rinsing withan organic solvent (e.g., PGMEA, PGME, 4M2P, CHX, EEP, nBA, etc.).

A photoresist 108 is then deposited onto the grafted polymer brush 104.This is illustrated at step 212. A variety of coating processes can beused to apply the photoresist 108. Examples of these coating processescan include spin coating, spray coating, dip coating, knife edgecoating, printing approaches (e.g., ink jet or screen printing), spincasting, etc. The application can take place in a single coating step ormultiple coating steps. Using multiple coating steps can provide greatercontrol over the coating process. For example, a series of spin coatingscan be used to provide a desired thickness, which can range from a fewnanometers to a few microns. After the photoresist is coated onto thepolymer brush 104 and substrate 112, further heating and/or solventevaporation steps can be carried out to harden the photoresist layer insome embodiments.

Following the formation of the photoresist layer 108, lithographicpatterning with extreme ultraviolet (EUV) light is carried out. This isillustrated at step 216. A variety of EUV light sources can be used. EUVlight sources for lithography generally have a high average power (e.g.,100 W or higher) at 2% bandwidth with a central wavelength of 13.5 nm.For example, a laser-driven tin (Sn) plasma with a high power drivelaser having a wavelength less than approximately 1 μm can be employed.In some embodiments, the drive laser is a pulsed laser. However, thedrive laser can also be a solid-state laser, gas-discharge laser, orexcimer laser. Examples of drive laser sources can includeneodymium-doped yttrium aluminum garnet (Nd:YAG), erbium-doped yttriumaluminum garnet (Er:YAG), ytterbium-doped yttrium aluminum garnet(Yb:YAG), titanium sapphire (Ti:Sapphire), neodymium vanadate(Nd:Vanadate), etc. It should also be noted that in some embodiments thepatterning can be carried out with electron beam (e-beam) lithography orimmersion photolithography, rather than EUV lithography.

A photomask with the desired pattern is used to partially mask thephotoresist before exposure to the energy source. Exposing thephotoresist to EUV light causes a chemical reaction to occur in theunmasked sections of the photoresist. When a positive photoresist withnegative tone development is used, the chemical reaction changes theunmasked sections from soluble to insoluble in the developer. However,when a positive photoresist with positive tone development is used, thechemical reaction changes the unmasked sections from insoluble tosoluble in the developer.

In order to promote the desired solubility switch, the process canoptionally continue with a hard bake (i.e., a post-exposure bake (PEB)).In some embodiments, the coating material is heated at temperaturesranging from about 45° C. to 150° C. However, the coating material canalso be heated at temperatures ranging from about 50° C. to 130° C. orabout 60° C. to 110° C. In some embodiments, the PEB is performed for atleast about 0.1 minute. However, the PEB can be performed from about 0.5minutes to about 30 minutes or from about 0.75 minutes to about 10minutes.

The soluble portions of the photoresist are removed by exposure to thedeveloper, followed by rinsing. In some embodiments, the developer isn-butyl acetate or an aqueous solution of tetramethylammonium hydroxide(TMAH). However, a dilute aqueous solution of sodium carbonate (Na₂CO₃)or potassium carbonate (K₂CO₃) can be used as a developer as well.Further, developers based on aqueous solutions of buffered sodiumhydroxide (NaOH), buffered potassium hydroxide (KOH), TMAH in water withadded surfactants, mixtures of NaOH and KOH, etc. can be used. Examplesof solutions or solvents for rinsing away soluble photoresist 108material after treatment with the developer can include deionized water,water with added surfactants, mixtures of water with miscible alcohols,etc.

The polymer brush 104 can be left on the inorganic hardmask (HM) 112.However, if the polymer brush 104 has cleavable groups, it can bepartially or completely removed from the substrate during or afterpatterning. Removing the polymer brush 104 is accomplished by applyingreaction conditions that will disrupt bonds at the cleavable groups.Examples of reaction conditions that can cleave these groups can includeacid, heat, photon radiation, etc. A combination of two or more of theseconditions can also be used. The resulting cleaved polymer can then berinsed away with an organic solvent.

Following the development of the photoresist 108, the pattern (i.e., thesections that were removed during development of the photoresist 108) isetched onto the inorganic HM 112. However, it should be noted that themethods described herein can also be applied to etching onto a siliconwafer or other substrate layers. Further, in some embodiments theinorganic HM 112 or other substrate is etched by reactive ion etching(RIE), though other examples of etching processes that can be used caninclude ion beam etching, plasma etching, laser ablation, etc.

FIG. 3 is a diagrammatic representation 300 of block structures 302,306, and 310 of three examples of generic polymer brushes, according tosome embodiments of the present disclosure. The generic polymer brushesrepresented by block structures 302, 306, and 310 each have somecombination of repeat units with grafting groups 314, cleavable groups318, and interface tuning groups 322. The functional groups 314, 318,and 322 are represented by a square, triangle, and circle, respectively.However, these shapes are for illustrative purposes only, and do notrepresent the actual approximate shapes of functional groups or monomersin the polymer brush. The molecular structures of examples of polymerswith functional groups 314, 318, and 322 attached are discussed ingreater detail with respect to FIG. 4.

The x, y, and z portions of the polymer chains in the polymer brushblock structures 302, 306, and 310 represent portions of the polymerchains having different types of repeat unit (i.e., repeat unitsprovided by different monomers and/or having different functionalgroups). The x portion of the first block structure 302 is a portion ofthe chain having repeat units with grafting groups 314, the y portion ofthe first block structure 302 is a portion of the chain having repeatunits with cleavable groups 318, and the z portion of the first blockstructure 302 is a portion of the chain having repeat units withinterface tuning groups 322.

The x portion of the second block structure 306 is a portion of thechain having repeat units with both grafting groups 314 and cleavablegroups 318, and the y portion of the second block structure 306 is aportion of the chain having repeat units with interface tuning groups322. The third block structure 310 represents an alternating copolymerhaving repeat units with grafting groups 314, cleavable groups 318, andinterface tuning groups 322. In some embodiments, the polymer brushesdisclosed herein have more than one type of each functional group 314,318, and/or 322 in one repeat unit. For example, a polymer brush 104could have both a phenol and a methoxy interface tuning group 322 in onerepeat unit.

It should also be noted that other combinations of monomers andfunctional groups are possible. For example, a polymer brush 104 couldhave one repeat unit with both grafting 314 and interface tuning groups322. Additionally, in some embodiments the polymer brushes 104 do nothave cleavable groups 318. Further, polymer brushes 104 can have morethan one of each chain portion. For example, a polymer brush representedby the block structure 302 could have, in addition to its x portion,other portions containing repeat units with grafting groups 314. Apolymer brush 104 can also include portions having repeat units withfunctional groups that are not grafting groups 314, cleavable groups318, or interface tuning groups 322.

The relative lengths of the polymer brush 104 chain portions (i.e., thenumber of repeat unit in the chain portion) can vary relative to oneanother. When the portion lengths are varied, properties of the polymerbrush 104 are affected. For example, increasing the number of graftinggroups 314 by lengthening the x portion relative to the y and z portionsof the first block structure 302 can increase the density of bindinglocations for grafting of the polymer brush 104 to the inorganic HM 112.Additionally, increasing or decreasing the number of interface tuninggroups 322 by lengthening the z portion relative to the x and y portionsof the polymer brush represented by the first block structure 302 canalter the nature of the interactions between the polymer brush 104 andphotoresist 108.

Further, the number of portions of a particular repeat unit can beincreased or decreased. For example, rather than increasing the lengthof the x portion of the polymer brush represented by the first blockstructure 302, additional chain portions having repeat units withgrafting groups 314 could be included to increase the density of bindinglocations. These chain portions could be x portions, or they could beportions of another repeat unit having the same or different graftinggroups 314. The length and frequency of chain portions can be controlledusing monomer choice and polymerization conditions.

FIG. 4 is a diagrammatic representation 400 of the molecular structuresof four examples of polymer brushes 404, 408, 412, and 416, according tosome embodiments of the present disclosure. The x, y, and z portions ofpolymer brushes 404 and 408 correspond to the x, y, and z portions ofthe first polymer brush block structure 302 illustrated in FIG. 3. TheR¹ groups in the x portions of polymer brushes 404 and 408 are substituents having at least one grafting group 314. The methyl ester groupin the y portions of the polymer brushes 404 and 408 is a cleavablegroup 318. The R² groups in the z portions of polymer brushes 404 and408 are acidic interface tuning groups 322, and the R³ groups can be ahydrogen atom, a methyl group, or a trifluoromethyl group.

The x and y portions of polymer brush 412 correspond to the x and yportions of the second polymer brush block structure 306 illustrated inFIG. 3. However, unlike the x portion of the second block structure 306,the x portion of polymer brush 412 does not include a cleavable group318. The x portion of polymer brush 412 has repeat units with R¹grafting groups 314, and the y portion of polymer brush 412 has repeatunits with phenol interface tuning groups 322. Polymer brush 416 is analternating copolymer that corresponds to the third polymer brush blockstructure 310 illustrated in FIG. 3. The carboxylic acid groups and R³groups on polymer brush 416 act as interface tuning groups 322. Further,the R¹ group is a substituent with at least one grafting group 314, andthe ester moiety is a cleavable group 318.

FIG. 5A is a chemical reaction diagram 500 illustrating processes 500-1and 500-2 of forming two example polymer brushes 508 and 516, accordingto some embodiments of the present disclosure. In these reactions, thepolymer brushes 508 and 516 are formed by binding alkyne grafting groups314 to pre-selected polymers. In the first of the two reactions 500-1, apoly(maleic anhydride) polymer 504 is a starting material for thepolymer brush 508. This poly(maleic anhydride) polymer 504 has an R⁴group that acts as an interface tuning group on the resulting polymerbrush. Examples of R⁴ groups can include phenyl groups, methoxy groups,ethylene groups, etc. In process, 500-1, the poly(maleic anhydride)polymer 504 is combined with 4-pentyn-1-ol, which is an alcohol with aterminal alkyne moiety. The mixture is reacted at approximately 120° C.for approximately two hours. This anhydride ring-opening reactionproduces a polymer brush 508 with an alkyne grafting group bound to anester moiety.

In the second reaction 500-2, polyhydroxystyrene (PHOST) 512 is combinedwith 6-iodo-1-hexyne and potassium carbonate (K₂CO₃) in an acetonesolution. The solution is heated to produce a PHOST-derived polymerbrush 516 with phenol interface tuning groups 322 on the repeat units inits x portion and alkyne grafting groups 314 on the repeat units in itsy portion. The x and y portions of the PHOST-derived polymer brush 516can be any length and can alternate in portions of identical length ordifferent lengths. Adjusting the stoichiometry of this reaction can varythe number of alkyne grafting groups.

FIG. 5B is a chemical reaction diagram illustrating a process 500-3 ofgrafting a polymer brush 508 to an inorganic hardmask (HM) 112, and aprocess 500-4 of cleaving the polymer brush 508 from the inorganic HM112, according to some embodiments of the present disclosure. In process500-3, the polymer brush 508 is spin coated onto the inorganic HM 112,and subsequently baked for approximately 1 minute at approximately 150°C. The baking promotes the covalent bonding of the alkyne graftinggroups 314 on the polymer brush 508 to the inorganic HM 112. Uponattaching the polymer brush 508, subsequent preparation steps can becarried out (e.g., photoresist application and lithographic patterning).In process 500-4, the polymer brush 508 is cleaved from the inorganic HM112. A combination of acid (H⁺) and heat are applied to the attachedpolymer brush 508 in order to break the bond between the grafting group314 and the remainder of the polymer brush 508. The residual polymer 504can then be rinsed away by an organic solvent.

The photolithographic processes involving the polymer brushes 104disclosed herein can be used in the fabrication of integrated circuitchips for use in electronic devices. These integrated circuit chips canbe distributed by the fabricator as raw wafers, bare die, packaged in asingle chip form (e.g., a plastic carrier with leads attached to amotherboard or other carrier), packaged in a multichip form (e.g., aceramic carrier with surface interconnections and/or buriedinterconnections), etc. The chips can be integrated with other chips,circuit elements, signal processing devices, etc. Examples of endproducts that can contain the chip include computing devices (e.g.,computer products including a display, keyboard or other input device,and processors), toys, appliances, automotive parts, etc.

In addition to improving the adhesion of a photoresist to an inorganichardmask 112, silicon wafer 116, or other substrate, the polymer brushes104 disclosed herein can be used for other purposes. For example, thepolymer brushes 104 could be used to improve adhesion between aninorganic surface and a non-photoresist polymer. The polymer brushes 104could also be used to improve wettability of a surface, preventbiofouling on underwater surfaces, improve the performance of ion beametching, etc.

It should be noted that, in some embodiments, the compounds describedherein can contain one or more chiral centers. These can include racemicmixtures, diastereomers, enantiomers, and mixtures containing one ormore stereoisomer. Further, the disclosed compounds can encompassracemic forms of the compounds in addition to individual stereoisomers,as well as mixtures containing any of these. Temperature and time rangesindicated herein can include the temperature or time on either end ofthe range, or any temperature or time between these limits.

The synthetic processes discussed herein and their accompanying drawingsare prophetic examples, and are not limiting; they can vary in reactionconditions, components, methods, etc. In addition, the reactionconditions can optionally be changed over the course of a process.Further, in some embodiments, processes can be added or omitted whilestill remaining within the scope of the disclosure, as will beunderstood by a person of ordinary skill in the art.

What is claimed is:
 1. A polymer brush, comprising: a plurality ofrepeat units; at least one portion of the plurality of repeat unitshaving one or more grafting groups, wherein the one or more graftinggroups are selected based on an identity of an inorganic substrate; atleast one portion of the plurality of repeat units having one or morecleavable groups, wherein the one or more cleavable groups do not bindto the inorganic substrate; and at least one portion of the plurality ofrepeat units having one or more interface tuning groups, wherein the oneor more interface tuning groups are selected based on an identity of aphotoresist.
 2. The polymer brush of claim 1, wherein the one or moregrafting groups are independently selected from a group consisting ofalkynes, primary hydroxyls, secondary hydroxyls, acrylic acids, epoxies,alkenes, phosphonic acids, propargyls, phosphonic esters, amines,carboxylic acids, and alkoxysilanes.
 3. The polymer brush of claim 1,wherein the one or more interface tuning groups are independentlyselected from a group consisting of an acidic group, a phenyl group, amethoxy group, an ethylene group, a hydrogen atom, a methyl group, and atrifluoromethyl group.
 4. The polymer brush of claim 1, wherein the oneor more cleavable groups are esters.
 5. The polymer brush of claim 1,wherein the one or more interface tuning groups mediate adhesion betweenthe inorganic substrate and the photoresist.
 6. The polymer brush ofclaim 1, wherein the inorganic substrate is an inorganic hardmask. 7.The polymer brush of claim 6, wherein the inorganic hardmask comprises amaterial selected from a group consisting of silicon, titanium nitride,titanium oxides, titanium oxynitrides, tantalum nitride, hafnium oxides,niobium nitride, lanthanum oxide, silicon oxides, silicon oxynitrides,zirconium oxides, and tin oxides.
 8. An electronic device, comprising:at least one integrated circuit chip prepared in an extreme ultravioletlithographic patterning process, wherein the extreme ultravioletlithographic patterning process comprises: providing an inorganicsubstrate; and depositing a polymer brush onto the inorganic substrate,wherein the polymer brush comprises: a plurality of repeat units; atleast one portion of the plurality of repeat units having one or moregrafting groups, wherein the one or more grafting groups are selectedbased on an identity of the inorganic substrate; at least one portion ofthe plurality of repeat units having one or more cleavable groups,wherein the one or more cleavable groups do not bind to the inorganicsubstrate; and at least one portion of the plurality of repeat unitshaving one or more interface tuning groups, wherein the one or moreinterface tuning groups are selected based on an identity of aphotoresist.
 9. The electronic device of claim 8, further comprising atleast one additional circuit chip.